A release device mounted in a bicycle includes a fork including a socket at a bent portion and two yoke arms extended downward from both sides of the socket to mount a front wheel at distal ends thereof; a sleeve fastened in the socket with an upper portion thereof projecting from the socket, the sleeve including at least one longitudinal top slit; an abutment tube including an upper extension passing a head tube to be threadedly secured to a stem; and a clamp put on an upper portion of the sleeve. The clamp is adapted to either fasten the sleeve and the abutment tube together by contracting the slit by exerting a force in a first direction or unfasten the sleeve and the abutment tube by exerting a force in a second direction opposing the first direction.